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NGV- 12, 1957 P. G. THORNHILL 2,813,016"

METHOD OF ROASTING NICKELIFEROUS SULFIDE CONCENTRATES IN A FLUIDIZED BEDFlled April 50,v 1954 2 Sheets-Sheet 1 "o loa-*@/olNvEN-ron l Philip G.Thornhill ATTORNEYS United States Patent O i METHOD F ROASTINGNICKELIFEROUS SUL- FEDE CONCENTRATES 1N A FLUIDIZED BED Philip G.Thornhill, Falconbridge, Ontario, Canada, as-

sxgnor to Falconbridge Nickel Mines Limited, Toronto, Ontario, Canada, acorporation of Canada Application April 30, 1954, Serial No. 426,754

18 Claims. (Cl. 75-9) This invention relates to the fluidized bedroasting of metal sulfide concentrates and has for its objectimprovements in the method of and apparatus for treating metal sulfidebearing slurries in roasting furnaces which operate on the fluidized bedprinciple.

More particularly, the present invention relates to the introductioninto a liuidized `bed roasting furnace of metal sulfide slurries whichcontain advantageously slime particles and/or water soluble materialswhereby the agglomerative action of the slimes and water solublematerials becomes an advantage rather than a detriment to the fluidizedbed operation. In other words, a specific object of this invention is toprevent the formation of oversized solid masses which would otherwiseaccumulate in the fluidized bed, and to form instead very smallagglomerates which present a number of process and treatment advantages.

ln the past, metal sulfide slurries have normally been pumped into thefluid bed roasting furnace through a horizontal feed tube located in thefurnace wall at a point below the Isurface of the turbulent bed or justabove it. Since, in either of these methods of introducing slurry intothe furnace, dehydration of the slurry must take place in the fluidizedbed itself, the turbulence of the bed is depended upon to effect thedisengagement of the individual particles comprising the masses ofslurry as the drying of the latter progresses. In other words, so longas water is the sole bonding agent in the slurry, its disappearancethrough evaporation in the roasting bed leaves the individual particlesfree to take their places as single entities in the fbed, supplying tothe bed new material having a particle size distribution substantiallyequivalent to that obtaining in the slurry. Thus when the normalsubstantially slime-free sulfide flotation concentrates are fed to theroaster bed as aqueous slurries containing no more water solublematerials than normally occur as residual tiotation reagents andimpurities, the conversion from slurry to discrete solid particles isuninterrupted, and While this results in relatively smooth operation ofthe roaster, dust carry-over is often inordinately high.

If, on the other hand, the slurry undergoing treatment contains certaintypes of slime materials and/or water soluble materials such as a saltor salts, the slurry, even after complete drying, fails to disintegratein the manner described above, and much of the new material thusintroduced to the bed agglomerates; the agglomerates tend to increaseinsize and to remain as oversized lumps which deuidize the bed and renderthe process inoperative. That is to say, the slimes and water solublematerials function as intergranular adhesives in the slurry masses,preventing the particles from being broken up by the turbulent action ofthe fluid bed, even after complete dehydration and subsequent roastinghave taken place. Not only is the adhesiveation of the aforementionedInaterials effective between fresh slurry particles, but it can alsocause agglomeration between freshly introduced slurry and the particlescomprising the iluidized bed to which it is 2,813,016 Patented Nov. 12,1957 added. In this way, the continued addition of such slurriesdirectly to the bed results in the formation of increasing proportionsof agglomerates which may be classed as oversize lumps in `the terms ofthe particle sizes desirable in tluidized beds employed for the roastingof sulides, viz., in excess of about 4-mesh. It can thus be readilyappreciated by those skilled in this art that the formation in thefluidized bed of increasing proportions of agglomerates larger thanabout 4-mesh can result only in eventual loss of fluidity in the bed andtermination of the roasting operation.

The formation of oversize lumps in the manner described above is furtheraggravated by either of the conventional methods of feeding slurries ofthe type with which this invention is concerned. For example, whenslimeor salt-bearing metallic sulde slurries are fed to a liuidized bedat a point below its surface, there is a tendency for hard, partiallyroasted accretions of sultides to form on the feed nozzle. Suchaccretions often cause blockage of the feed tube, upsetting the smoothoperation of the roaster. More serious, however, is the effect of theseaccretions on bed fluidity, since they break off and accumulate in thebed with the other deiiuidizing oversize lumps. On the other hand, whensuch `a slurry is fed horizontally into the furnace at a point above thesurface of the uidized bed, a considerable proportion of the slurrysimply falls, or drips from the mouth of the feed tube, which isnecessarily located near the roaster wall. The part of the bed near thiszone is somewhat less mobile than the center of the bed because of aso-called wall effect, and it is, therefore, particularlydisadvantageous that slurry should fall at this point. Moreover, sincethe gases surrounding the feed nozzle are at a temperature approachingthat obtaining in the roasting bed, the dripping slurry results in agradual build-up of hard, caked material on the nozzle. The caked nozzleaccretion falls into the bed, further decreasing its mobility an-dfluidity. As this process is repeated, bed turbulence near the feednozzle is eventually brought to a standstill, and the result is a moundof raw, caked sulfides eX- tending from the bed to the feed tube, andwhich grows outwardly from the wall toward the center of the bed asoperation continues. This inactive mound reduces the effective heartharea, and hence the capacity, of the furnace. The introduction ofcompressed air along with the slurry in the feed tube does little toalleviate this condition, and has the added disadvantage of oftenimparting sufficient Velocity to the slurry to carry it to the oppositewall of the furnace, where it builds up in the form of hard cakes of rawsulfides which eventually fall into the bed, contributing further to itsloss in tiuidity.

The deleterious eifects of slime or water soluble materials such assalts in the sulfide slurry fed to the tluidized bed roasting furnaceare cumulative in nature since the turbulence of the fluidized bed isthe sole agent by which the initially oversized accretions oragglomerates might be broken up when slurry is fed directly to the bed.The presence of these accretions in the fluidized bed causes adeterioration in bed fluidity or turbulence, which in turn not onlyincreases the tendency for more agglomerates to form, but also decreasesthe likelihood of their being broken up, having once formed. Suchcumulative deterioration results eventually in complete loss offluidity, and the roaster must be shut down and cleaned out.

Investigations have led to the discovery that such operationalditliculties can be overcome for the most part and that other advantagescan be gained when proceeding in accordance with the present invention.

The invention contemplates the roasting of metal sulde concentrates in auidized bed, in which a slurry is prepared by mixing metal sulfideconcentrates and slimes drying stage the salt solution reaches aconcentration where it functions as a binding agent to form in situagglomerates of the concentrate particles. The newly formed agglomeratesare kept in suspension in the freeboard space long enough thoroughly todry them before they reach the fluidized bed. The agitation orturbulence of Ithe bed and hence of the agglomerates is suicient toprevent them from adhering `or sticking to one another, ensuring thatthe particle sizes in the bed fall within the optimum range, not largerthan about 6-mesh.

The fluidized bed roasting of .the dry agglomerates formed in situ iscarried out within an optimum tempera ture range. A temperature notlower than about 600 C. and not higher than about 700 C. has givenexcellent results. The roasting reactions take place autogenously andthe control of the temperature is effected by the adjustment of the feedrate and, if necessary, by the injection of water into the freeboardzone. The rate of ow of air into the iluidized bed is `at least as greatas that required by the feed rate on the basis of the desiredstoichiometry, and tests indicate that calcines satisfactory to theprocess can be produced when the rate of air flow exceeds this value byas much as 300 percent.

The particular advantages afforded by the employment of agglomerates ofpyrrhotite concentrate particles held together by a network of sodiumsulfate become more evident when the behaviour of such agglomerates in ailuidized bed is considered. So far as the mechanics of the iluidizedbed is concerned, each `agglomerate is a separate entity, and, as such,is subject to the uniformity of temperature and gaseous environmentobtained by the constant turbulence of a iluidized bed. On the otherhand, the particles comprising the agglomerate remain in contact withthe same bonding network of salt throughout the entire treatment, asituation of prolonged contact which is essential to the successfulfunction of the sodium salt in its capacity as a chemical reagent. Inspite of the eflicacy of the salt as `an inter-particle bonding agent inan individual agglomerate, there is no tendency for the agglomerates tobecome attached to one another during the uidized bed roastingtreatment. In other words, the agglomerates do not cake up Iand causeloss of iiuidity in the bed.

The selective sulfate roasting of the nickeliferous pyrrhotite is basedupon the thermodynamic relationships existing between the sulfates ofthe metals present in a concentrate which is rich in this mineral. Underpractical roasting conditions the thermodynamic stabilities of the metalsulfates decrease in this order: cobalt, nickel, copper and iron. Sincethe stabilities of these sulfates are direct functions both of thetemperature and the partial pressures of the oxides of sulfur present inthe system, the proper control of these variables can result in a systemin which the sulfates of cobalt, nickel and copper are stablethermodynamically, while those of iron are not. Moreover, if thepyrrhotite and other contained metal sulfide minerals are made toundergo the roasting reactions at a satisfactory rate in the samesystem, the end products of such reactions are calcines consistingsubstantially of iron oxide and the sulfates of cobalt, nickel andcopper. In other words, the iron is rendered waterinsoluble while thecobalt, nickel and copper are rendered water-soluble.

The cobalt and copper suldes in the pyrrhotite concentrates can beconverted to their sulfatos, and thus be rendered water-soluble, quitereadily when such concentrates are roasted under suitable conditions oftemperature and gaseous environment. The nickel sulfide, as pointed out,shows a strong tendency to avoid sulfate formation. Its refractorynature appears to be due to such causes as the following:

(1) The ability of the nickel sulde to form relatively stable nickelferrites of variable composition; and

(2) The kernel roasting effect by which the nickel in an iron-nickelsulfide particle tends to become concentrated in the residual sulfidecore of the hot particle as roasting proceeds. The progressive increasein the proportion of nickel in the residual sulfide is accompanied by adecreasing tendency for the nickel sulfide to participate in therequired roasting reactions. This is due, in part, to the more denselyprotective nature of the iron oxide which is formed during the latterstages of the oxidation of the particle. The effect is a direct functionof particle size. That is to say, the smaller the concentrate particlethe less is the kernel roasting effect, thus assuring substantiallycomplete conversion of the nickel sulfide in the particle to the desirednickel sulfate during lthe roasting operation. Such conversion isassured when using extremely fine concentrates, with a particle size,for example, as small as or no larger than that herein specified.

While the principle of particle size reduction is employed widely whenan increase in reaction rate between solids and gases is desired, theend in the present invention is not so much an increase in reaction rateas the prevention of the selective oxidization of the nickel bearingiron suliides which results in the kernel enrichment. The effect ofkernal enrichment is cumulative, for as the iron in a concentrateparticle is removed from the nickel sulfide to form an iron oxidecoating, there is a tendency for the kernel to achieve such aconcentration in nickel as to provide a nickel to iron ratio approachingthat which, when oxidized, would form dense protective nickel ferritelayers between the nickel sulde and the iron oxide coating. Also,suliides high in nickel are much more diflicult to oxidize than suliideslow in nickel.

An even more important advantage afforded by the employment of extremelyfinely divided pyrrhotite particles is their amenability toagglomeration, which is essential to the practice of this invention. Aswill be shown later, this tendency for finely ground pyrrhotiteconcentrates to form agglomerates is enhanced by the .binding action ofthe added sodium sulfate.

In general the tests indicate that the concentration of the saltadditions necessary appears to depend, to some extent, upon theconcentration of nickel in the pyrrhotite. The primary chemical functionof the sodium sulfate is to render unstable the ferrites of nickel. Thisis probably eifected by an exchange between the sodium sulfate andnickel ferrite similar to the reaction expressed by the followinghypothetical equation:

From the above, it can be seen that the effective functioning of thesodium sulfate depends largely upon the intimacy of contact between thatsalt and the roasting sulde particles as well as on the maintenance of agastemperature relationship which provides conditions under which nickelsulfate remains stable. Thus, while the required amount of sodiumsulfate addition to the pyrrhotite depends on the concentration of thenickel, that portion of the sodium sulfate which is effective in theabove reaction is limited by the extent to which it remains in contactwith the roasting ore particles. As will be shown later, this limit isreached with NasSO4 additions of about ve percent by weight of drypyrrhotite concentrate, beyond which proportions further additions areineffective because of particle surface limitations.

The sodium sulfate also acts as a carrier, or in a sense a catalyst, forthe sulfating reaction. Sodium sulfate, Na2SO4, in the furnace, takes onS03 formed by the oxidation of SO2 as it passes mixed with excess airthrough the bed.

Sodium pyrosulfate is thus formed, which is in itself a vigoroussulfating agent.

The stability of the pyrosulfate is an inverse function of temperatureand a direct function of the concentration of S03 in the gasessurrounding it. Qualitatively, similar conditions hold for the sulfatesof nickel, cobalt and .e7 copper. For the sake of simplicity thefollowing two equilibria may be abstracted for consideration.

The nickel sulfate is more stable than the sodium pyrosulfate indicatedby the reactions. It may be assumed that one of the agglomerates, forexample, in the course of its roasting treatment, encounters varyingconditions of temperature and S03 concentration, or, in other words,conditions that are not always favorable for the formation of sulfates.It seems reasonable to suppose then that, while the agglomerato is in azone favorable to sulfation, both reactions (l) and (2) progress to theright, to form both sodium pyrosulfate and nickel sulfate. When such anagglomerate moves to a less favorable zone, reaction (l) is reversed,thus restoring the concentration of S03 necessary for the progress ofreaction (2) to the right. ln this way the sodium sulfate acts as asulfur trioxide, S03, reservoir or buffen ensuring adequate localconcentration of the sulfating agent. This is, of course, in addition tothe role of sodium in preventing the formation of ferrites.

Such fines as do result from the roasting operation are advantageouslyreturned to the iiuidized bed. The nes themselves may be separated fromthe gaseous mixture arising from the bed in any suitable manner, such asby passing the mixture through one or more cyclones. The nes recoveredby the cyclones may be returned, for example, by forcibly injecting themby means of an enclosed screw conveyor into the bed. The return of thelines to the bed offers several important advantages: First, it helps tomaintain a small, but essential, proportion of fine material in the bedto assure conditions favorable to the maintenance of fluidity. Second,it permits enrichment of the fluidized bed with additional amounts ofsulfating gases. These gases result from the decomposition at bedtemperature of iron sulfates which have formed during the passage of thedust through the cooler zones of the system, such as the furnacefreeboard, or open space, above the bed and the ducts to and through thedust recovery system. Third, particles in the dust which haveshort-circuited the fluid bed treatment by premature entrainment in thegases are returned for further roasting and sulfating treatment in thebed.

As already indicated the calcines resulting from the selective sulfateroasting operation consists of agglomerates of material which retainsubstantially their original geometric identity. The calcineagglomerates can undergo subsequent handling, including a water leachingoperation, without losing their shape or hardness. All of the watersoluble material can be extracted from them by aqueous treatment withoutthe necessity of subjecting them to any further treatment, such asgrinding or other form of disintegration. This affords a distinctadvantage over the conventional type of calcine obtained from finelyground nickel suldes in that all of the subsequent steps in the process,such as leaching, filtration and drying, are greatly facilitated by thepresence of relatively small proportions of tine material. v

These and other features of the invention may be better understood byreferring to the accompanying drawing, taken in conjunction with thefollowing description, in which Figure l is a diagrammatic sideelevation, partly in section, of a form of apparatus illustrative of apractice of the invention;

Figure 2 is a section on the line 2-2 of Figure l, showing the hearth ofthe roaster;

Figure 3 is a section on the line 3-3 of Figure l, showing the top ofthe iiuidized bed on the hearth;

Figure 4 is a section on the line 4 4 of Figure 2, showinga wind-boxbelow and a plurality 'of air-distributors above the-hearth; and

Figure 5 is an enlarged fragmentary detail from Figure 4, showing a fewof the air-distributors immediately adjacent a discharge conduitextending from the hearth through a wind-box.

Referring trst to Figure 1, the apparatus shown includes a valved slurryfeed line 10 depending over a constant head tank 12, provided with anoverflow line 14 near its top to maintain a constant level 16 of slurry18 in the tank. Connecting the bottom of the tank is a discharge line20, a slurry pump 22 and a valved slurry feed line 24, titted with acoupling 25. An air line 26 connects an air compressor 28 with theslurry feed line. The slurry feed line in turn extends verticallythrough a removable cover 30 on a hood 32 mounted centrally around aman-hole 33 on the top of a roaster 34.

The tluidized bed roaster shown diagrammatically is generallyrectangularin elevation and cross-section, being formed of insulated(Figures 2 and 3) side walls 36 and 38, end walls 4t? and 42 and a roof44 (Figure l). The roasters hearth 46 (Figures 1 and 2) includes threeremovable plates 48, 50 and 52, on the tops of which are secured aplurality of spaced and raised air-discharge nozzles 54.

The bottom of the roaster terminates in an air distributor or wind-box56 (Figures l and 4), which is generally triangular in vertical-section(Figure 4). It is formed of side walls 58 and 60 and end walls 62 and64. An air distributor line 70 (Figures 1 and 2), with a valve 72,extends along the far side of the box. Branch outlets 74, 76 and 78connect the distributor line with three compartments 82, 84 and 86formed by partitions 88 and 90 (Figures l and 2). The branch inlets areprovided with valved meters 92, 94 and 96 (Figure 2) to regulate andmeasure the amounts of air introduced into the compartments.

Hearth plates 48, 50 and 52 (Figure 2) extend across the compartmentsand are fitted, respectively, with centrally -disposed `discharge pipes100, 102 and 184, the upper ends of which extend slightly above theplates (Figures 4 and 5). The discharge pipes depend vertically throughand below compartments 82, 84 and S6, being fitted with valves 106, 10Sand 110, respectively. Each compartment is fitted near its -bottom(Figure 4) with a valved discharge pipe 114 for the removal of solids.

The roaster is provided (Figure l) with a calcine discharge conduit 116in end wall 40, being located to maintain an optimum predetermined level118 of a fluidized bed 120 of agglomcrated material undergoing treatmentbelow freeboard space 122. A gas-fines discharge duct 124 connects thetop portion of the'roaster vwith a gasfines separator 126, such as acyclone. The cyclone advantageously connects a second gas-finesseparator 128, such as another cyclone, by means of a pipe 130. A stack132 extends from the second cyclone to the open atmosphere.

It is `advantageous to return the fines, separated from the roastergases in the cyclones, to the roaster for retreatment. To this end(Figure 1) down-comers 134 and 136 extend from cyclones 126 and 128,respectively, to a lateral feed tube 138 fitted with a power-drivenscrew conveyor 140. The discharge end of the tube connects with thelower portion of uidized bed 120.

Air-discharge nozzles 54 may be of any suitable design. The ones used inthe present apparatus are illustrated to better advantage in Figure 5.kThey are in the form or" standard pipe couplings or'fittings 144mounted on the upper ends of pipe nipples 146 secured to plates 48, Siland 52 in the manner shown. They-are secured at their lower ends inholes 148 spaced at 4" centers inA plates 48, 50 and 52 in the mannershown. The upper ends of the nipples lit into vertical portions 150 ofthe couplings. The upper ends of the vertical portions .are closed withplugs 152; andthe lower ends ofthe :inclined portions 154 9 of the'couplings are ttedwith similar plugs 156, each of which is provided,however, with a centrally disposed small jet hole or passageway 158 forthe escape downwardly, at an acute angle to the vertical, of very finestreams of air. Although not so shown on the drawing, in the presentpractice the jets face in the same direction.

Since passageways 158 point downwardly, lines from the bed of uidizedmaterial cannot fall into and clog them. Also, since the plugs 156 arelocated above the hearth plates, the material near the plates isunaffected by the fluidizing gases, and remains static when calcines areremoved through calcine discharge conduit 116. This results in a deadoverall layer 160. This is beneficial because the layer acts to insulatethe plates. As will be pointed out below this overall layer in turn maybe considered as formed of an over layer 162 of normal size agglomeratesand an under layer 164 containing oversize agglomerates, if present. Thelayers tend to shift relatively to each other, in size and contourduring operations.

One or more heaters 180, 182, such as oil or gas-burners, are associatedwith the roaster to bring the chamber to temperature to initiate theroasting operation. The heaters are located advantageously just abovethe surface of bed 120.

It is highly desirable to be able to control the temperature of theoperation, the bed as well as the freeboard. Since the roasting takesplace autogenously, exothermic heat is released in the bed and riseswith the roaster gases into the freeboard. Some control of thetemperature of the bed may be eifected by varying the rate at which theslurry is fed above and air is introduced below the hearth of thefurnace. To lower the bed temperature it has been proposed also to wetit with water, a stream of water being played onto or released in thebed for the purpose. This is objectionable, however, because the dampmaterial tends to lump and hence to deuidize the bed. That result may beavoided by introducing one or more streams of water into the freeboardspace, and evaporating all of it before it reaches the bed.

To this end the apparatus (Figure 1) may include, for example, a valvedmain water supply line 190, having a coupling 192, which connects with alateral distributor line 194 having valved branch feed lines 196, 198and 200. Side branch lines 196 and 200 extend vertically through theperipheral portion of man-hole cover 30, their open free ends 202 and204 being directed outwardly so that streams of water 206 and 208sprayed therefrom may be directed away from and generally along the sideof the conical slurry'stream being sprayed from feed line 24. The wateror liquid composition, and hence the viscosity, of the slurry is notaltered substantially when operating in this manner. Mid branch line 198connects slurry feed line 24 so that, if desired, additional water maybe added to the Vslurry with which toy cool the freeboard. Theconstruction shown has the advantage that couplings 25 and 192 permitthe slurry and the water branch lines to be removed with the cover as aunit. Water feed lines may be led into the freeboard at any othersuitable place in its top or upper portion; the requirement `being thatthe sprayed water must have suicient time during its descent to beevaporated before reaching the fluidized bed.

Closeable openings, not shown, are provided in the chamber Walls, atvarious levels, for the introduction of calcined starting material, forthe insertion of thermocouples to determine and regulate thetemperatures of the bed and open space above the bed, for observationand inspection, etc.

The apparatus described may be operated as follows:

Previously calcined agglomerates of the concentrates are fed to theroaster through one or more of the closeable openings, not shown, tobuild up'a starter-bed. Such a bed is necessary to initiate the roastingoperation to follow. That is to say, the material to be roasted must" bemixed in the roaster with material that has already been roasted. Priorto the introduction of raw sulde concentrates, the starter bed must beheated to a ternperature suiiiciently high to permit the roastingoperation to be self-sustaining. To this end (Figure l) oil or gasburners 130, 182 are used to provide the preliminary heat. When the bedhas achieved the temperature required to initiate the combustion of thesuldes, the burners are shut off.

Slurry 1S is formed by mixing the concentrates with a water solution ofsodium sulfate, after which it is passed (Figure l) through feed line 10into tank 12. A suiiicient amount is fed into the tank to cause acontinuous overflow of slurry through line 14 to maintain the body ofslurry in the tank at predetermined level 16. Pump 22 is operated at apredetermined constant speed while compressor 28 delivers air underpredetermined pressure to slurry feed line 24. Variables involved in theoperation are controlled to cause the slurry issuing from the feed lineto spread and spray downwardly into freeboard space 122. Since thisspace is highly heated, the sprayed slurry undergoes immediate drying,causing the concentrate particles to agglomerate while in transitthrough that space` it may be helpful to consider in more detail whathappens to slurry 13 as it issues from feed line 2d on its path oftravel toward bed 120. Since the free and open end of the feed linedepends vertically into freeboard 122, at its toprnost portion, thesluiry is sprayed downwardly and laterally, at least initially, in acone-like stream through the rising highly heated roaster gases from thebed. As the slurry spreads out it is broken into a multitude of minutedroplets or globules. Some of them are formed of freed slurry liquid andothers are formed of concentrate particles held together by retained orcontained slurry liquid. That part of the path of travel (Figure l) maybe referred to for convenience as zone A. Due to the elevatedtemperature of the freeboard, some of the freed slurry liquid and someof the retained slurry liquid undoubtedly is there vaporized; but thiszone may be regarded essentially as the freeboard area in which thesprayed slurry is broken up into minute droplets.

The droplets descend into and through what may he considered as zone B.Here much if not all of the remaining freed slurry liquid is evaporatedand removed from the freeboard via duct 124; and wet agglomerates of theconcentrate particles are formed in situ while in transit through theZone. Some of the slurry liquid retained by the agglomerates is boiledoff.

Such freed and retained slurry liquid as remains is evaporated as theWet agglomerates enter and pass through what may be called zone C,immediately above the uidized bed. Here the agglomerates fall throughthe rising roaster gases at just about their highest temperature and arethoroughly dried before they reach the bed.

It will be understood that what has been said is intended as a generalexplanation of what appears to occur. There is no clear-cut boundarybetween the zones, obviously; there must be some overlapping. But, inany event, the path of travel pursued by the slurry as such, itsresulting droplets and agglomerates, through the freeboard is so long,so extended, as to provide ample time for the slurry liquid, both freeand retained, to be evaporated and for the agglomerates to becomethoroughly dried before they reach the bed. In other Words, no liquid ispermitted to reach the bed, by way of the slurry or in any other way.All of the slurry liquid is vaporized in transit; its vapors mix withthe rising roaster gases; and the gas-vapor mixture is removedcontinuously from the upper portion of the freeboard by way of duct 124,cyclones 126 and 12S, and stack 132 to the open air.

Furthermore, the slurry liquid and the wet or damp agglomerates performanother `highly useful function during their short-lived period oftravel, that of intercepting, catching and returning a very substantialamount of dust or powder-like fines to the roaster bed. The slurry andagglomerates tend to act like a moving filter. Dust particles areentrained by the slurry liquid. Such entrained dust may in turn becomeattached to wet concentrate agglomerates or indeed may be converted intodust agglomerates which fall to the bed. A substantial amount of thedust particles as such come in contact with and are attached to thefalling wet or damp concentrate agglomerates, often becoming an integralpart thereof. Such dust as is not returned to the bed finds its way toduct 124 and cyclones 126 and 128; but the dust that is entrained isthoroughly dehydrated en route to the bed.

Every precaution is thus taken to assure a dry bed of agglomerates, inwhat may be designated as zone D, thus preventing them from bonding, dueto the presence of moisture, into oversize lumps which would operategradually to deiluidize the bed. For this reason the freeboard spaceshould be rather high, so that the period of suspension of the fallingslurry and'agglomerates will be suthciently long to permit theevaporation of all of their liquid or moisture. To this end it is betterto err on the side of having the height of the freeboard space somewhathigher than is necessary normally to effect the desired dehydration.

As shown in Figure 3, the agglomerates dried in transit strike the topof the bed 120 in a well-defined generally circular area 136, which iseasily observable through a peep-hole when the bed is quiescent. Thespray pattern is formed by spraying the feed through the freeboard for afew seconds while the bed is quiescent, and allowing the driedagglomerates to ignite on the hot surface of the dead bed. The glowingof the freshly deposited agglomerates delineates the spray pattern, andpermits adjustments to be made in the spray tube settings, etc. foroptimum spray conditions.

Air under pressure is passed simultaneously through distributor line 70(Figure 2) and branch outlets'74, 76 and 78 into compartments 82, 84 and86 in air distributor or wind-box 56. The amounts of air may be variedas between the compartments by means of valved meters 92, 94 and 96, ifdesired, or they may be maintained substantially the same. The air inthe compartments issues from the numerous air nozzles S4 above hearthplates 48, 50 and 52 in an equal number of tine streams. These manystreams of air keep the finely divided agglomerates in the bed in aturbulent .agitated state, thus facilitating the mixing of the new withthe old agglomerates and providing intimate contact of the air with theagglomerates. Each agglomerate in effect is enveloped in and supportedby air and the gaseous products of the roasting reactions, thusestablishingan environment conducive to oxidation of the suldes in theconcentrate particles.

When in full operation, calcined agglomerates are withdrawn from the bedas fast as freshly formed agglomerates from the sprayed slurry aredeposited on the bed. The calcines gradually find their way to and dropby gravity into and through discharge conduit 116.

The roasting operation requires a considerable amount of air, as aresult of which a large amount of sulfur gas, SO2 and S03, is formed.All of the water in the slurry is converted to steam. The sum total ofair, gas and steam is quite substantial and is Withdrawn continuouslyfrom the freeboard space. Some fines, lalthough a relatively smallamount, are produced necessarily `during the roasting operation. Some ofpowder-like proportions tend to become entrained in the gases. Theresulting gasnes mixture passes (Figure l) through duct 124 to firstcyclone 126, where a substantial amount of the heavier fines isseparated. The thus partially denuded gases pass into second cyclone 128where a substantial amount of the lighter fines are separated. The gasesleave the last cyclonerin the series for .stackV 132, from which theyare vented into the open atmosphere.

. through down-comers 134 and 136 into feed tube 138 where they arepropelled by screw-conveyor into bed 120 ofthe toaster.

The calcines that are continuously produced play an important part inthe chemical reactions that take place during the selective roastingoperation as :a whole. Iron oxide in the highly heated calcines in theturbulent bed functions as a catalyst promptly to convert freshly formedSO2 to S03 and thus aids very substantially in the conversion of thewater insoluble sulides of nickel, cobalt and copper to theirwater-soluble sulfate form.

In case oversize lumps are formed by fusion, either during the initialformation of the agglomerates above the bed or during their roasting inthe bed, they tend to settle to the bottom of the bed and sooner orlater find their Way, by reason of the action of the many iine streamsof air, into and through (Figures l, 4 and 5) over layer 164 into underlayer 160, and eventually into discharge pipes 100, 102 and 104. Theirvalves 106, 108 and 110 may be opened from time to time to withdraw theoversize agglomerates.

Instead of withdrawing calcined agglomerates from discharge conduit 116(Figure l), they may be withdrawn through one or more of discharge pipes100, 102 and 104. If desired the calcines may be withdrawnsimultaneously from the discharge conduit 116 and from one or more ofthe discharge pipes.

As Figures l, 4 and 5 clearly indicate, jet openings or passageways 158in nozzles 54 are held well above the level of hearth plates 48, 50 and52 for the purpose of preventing turbulence of the calcines on `and nearthe plates, regardless of whether the material is made up of oversizeagglomerates or not. Dead layer 160 supplants the conventional type ofrefractory insulating material (brick or castable refractory) and hasthe advantage over these of being easy to remove from the hearth plates,facilitating dismantlement of this part of the furnace for maintenance,etc.

Irregular under layer 160 (Figures l, 4 and V5) is intended to representgenerally the configuration assumed by that part of the overall staticlayer which may consist in part of oversize agglomerates, particularlywhe discharge conduit 116 isemployed for the removal of calcinedagglomerates. The conical depressions formed when withdrawals ofoversize agglomerates are made through tubes 100, 102 and 104 are filledwith regular calcines which sink down from the bed proper and becomeimmobile. When more oversize agglomerates are formed, they sink towardthe bottomY plates, thus repeating the process of displacement ofregular calcines.

The results just described may be facilitated by suitable adjustment ofa number of variables, such, for example, as the pressure of the airjets, the size of the jet openings, their angle of inclination, theirdirection with respect to each other, etc. VThe jet openings may berotated in a horizontal plane, by rotating ttings 144 or nipples 146, orboth. A

When, as is seldom the case, it is advisable to remove solids that mayhave found their way into compartments 82, 84 and 86, they may bedropped by gravity (Figure 4) through valved discharge pipes 114.

As indicated above, some temperature control of the freeboard and henceof the bed may be had by spraying water specially into the freeboar'd.To this end (Figure l) one or more streams of water may be sprayed fromside branch feed lines 196 and 200 downwardly into the top portion ofthe freeboard, and preferably to the side of the conical stream ofslurry being sprayed from slurry feed line 24 so as not -to impairsubstantially the composition of the slurry liquid especially in respectof its salt content. Or, if desired, the sprayed watermay be permittedto strike the sprayed slurry at any suitable stage during its descent.Also, 'if desired, extra water may be introduced into the slurry by wayof mid branch feed line 198, thus diluting the slurry withcoolant beforeit is sprayed into the freeboard. One or more of such expedients may beemployed. 'I'he path of travel of the added water through the freeboardis sufficiently extended to assure evaporation f all of the water beforeit can reach the bed, so that the bed will not be wetted by such water.`The Water vapors join the other vapors and gases making their exitthrough duct 124. 'Ilhe specially added Water thus cools the freeboarddirectly and the bed indirectly. It also functions to filter out dust inthe rising roaster gases.

In a presently preferred practice the calcines resulting from theselective sulfate roasting operation are subjected to a water leachingtreatment in a continuous countercurrent decantation system. Theaddition of acid, is not necessary or desired for the purpose. Thesolids are recovered separately and dried. The liquid or filtrate alsois separately recovered.

The liquid or filtrate portion, of course, contains the water solublesulfates of nickel, cobalt and copper, and may be treated in anyconventional manner to recover together or separately its nickel, cobaltand copper values. The sulfate solution may be treated, for example,with soda ash, NazCOa, to precipitate the nickel, cobalt and coppercarbonates. The resulting co-precipitates are suitably filtered, leavinga filtrate rich in sodium sulfate which is re-used as a bonding andsulfating agent for further amounts of the concentrates.Other'precipitants may be used, such as lime, limestone and causticsoda. Various procedures may be employed to precipitate the metalseither separately or in bulk. Sodium precipitants are particularlyadvantageous because the sodium may be converted into sodium sulfate toassure an. adequate supply of this salt for the treatment of furtheramounts of the concentrates. Since the operation is conducted, normallyat least, at a nickel smelter, the co-precipitate can be smelted with acharge of nickeliferous material to produce matte, which is in turntreated in the usual manner to recover separately the nickel, cobalt andcopper, or the nickel and cobalt together.

The leaching operation is conducted carefully and with sufficient waterto `separate the Water soluble sulfates therefrom. ln this manner thefinal solid residues will be practically free of the sulfates of nickel,cobalt and copper, thus leaving an agglomerated product, almost free ofslimes, that is substantially Wholly iron oxide. A clean-cut separationis thus obtained between nickel, cobalt and copper on one hand and ironon the other hand.

To determine the effect of sodium sulfate, as Well as its method ofaddition, on the metal extraction resulting from the sulfate roastingtreatment, a series of fluidized bed roasting tests were performed onpyrrhotite concentrates having the following chemical analysis:

Cu Ni S Fe Oo Insol. SiO;

Per- Per- Per- Per- Per- Per- Percent cent cent cent cent cent cent 0.30 1. 29 34. 4 52. 6 064 7. 6 5. 0

In some of the tests the pyrrhotite concentrate was roasted withoutbenefit of sodium sulfate or any other chemical reagent. In va secondgroup of tests, sodium sulfate was added with the pyrrhotite to form adry solids mixture, and in a third group of tests a similar proportionof sodium sulfate was added to the pyrrhotite concentrate as an aqueoussolution. Since the pyrrhotite concentrate employed in eachgroup oftests was identical in every respect, and since roasting'conditions werealso identical, the average nickel extraction gures for each groupclearly point up the importance of the sodium salt to the selectivesulfate roasting of pyrrhotite, as

follows:

The extraction figures refer to the proportion of the contained nickelwhich was rendered water soluble by the roasting of the pyrrhotiteconcentrate.

The pyrrhotite concentrate employed in the above group of tests wasground to a fineness such that 60% by weight could be passed through aZOO-mesh screen. When the same concentrate had been further comminutedso that could be passed through a 20G-mesh screen, treatment of theconcentrate with an aqueous solution of sodium sulfate to give a mixturecontaining 8% of the salt on a dry weight basis, followed by sulfateroasting in a fluidized bed yielded a calcine from which 91% of thecontained nickel could be extracted by water leachmg.

The eectiveness of the agglomerating action described earlier may bestbe shown by the particle size distribution of calcines resulting fromthe fluid bed roasting of pyrrhotite flotation concentrate according tothe novel feeding technique with which this invention is concerned. Thepyrrhotite concentrate employed was re-ground to such a fineness that97% by weight of dry concentrate could be passed through a ZOO-meshscreen, and which therefore contained a high proportion of colloidal ornear colloidal particles usually described as slimes. The finely groundpyrrhotite concentrate was mixed with water in such proportions as toprovide a slurry containing about 70% by weight of dry concentrate and30% of water substantially free from water soluble materials.

The slurry was fed to a fiuidized bed roasting furnace by pumpingthrough a tube made from a section of standard 1A pipe which projectedvertically downward through the furnace roof. The slurry was introducedat a rate of approximately 5 lbs. per minute, and was accompanied bycompressed air passing through the same tube at a rate of about 4`standard cubic feet per minute. The freeboard height, that is thevertical distance between the surface of the uidized bed and the furnaceroof was approximately l2 feet. Since the slurry feed tube projectedsome 6 inches below the furnace roof, the sprayed slurry particles weresubjected to a fall of about lll/2 feet before reaching the surface ofthe fluidized bed. Turbulence or fluidity of the bed was maintained byintroducing air at the bottom of the bed at the rate of approximately 23standard cubic feet per minute per square foot of hearthV area. Thetemperature of the freeboard gases was about 550 C., while that of thefluidized bed was held at about 675 C. The relatively minor amounts ofdust which escaped with the furnace gases were passed through two stagesof cyclone dust collectors, and the dust recovered thereby wascontinuously returned to the fiuidized bed by means of a screw feedmechanism. The calcine product was continuously withdrawn from thefluidized bed at such a rate that the level of the bed remainedsubstantially the same throughout the entire operation. Table I givesthe screen analysis of the calcine product.

lrelatively small.

The calcines for which the random particle size dis-- tributions arereported in Table I proved to be ideal for the maintenance of goodfluidity in the bed and for smooth continuous operation of the uidizedbed roaster, even though it is evident from the same screen analysisthat the proportion of material tine enough to be entrained in andcarried over by the furnace gases was Referring again to the screenanalysis of the pyrrhotite feed (97%-200-mesh) it is also evident thatatleast 75% of the feed had agglomerated to a particle size greater than200 mesh still leaving room for agglomeration in sizes below 200 mesh,and indicating that slurries of these types would be extremely likely toform oversized agglomerates or lumps if fed below or directly above thesurface of the fluidized bed in the conventional manner. On the otherhand, if the finely ground pyrrhotite had been filtered, dried, and fedto the roaster in the form of finely divided solids, agglomeration wouldhave been negligible, and the resulting calcines with their highproportions of fine material would have been susceptible to inordinatelyhigh dust carryover and, consequently, relatively high dust losses.

During the course of the chemical reactions which take place between theagglomerates and the gases in the fluidized bed, each individualagglomerate behaves physically as a separate unit, even though it ismade up of many minute concentrate particles which are interstitiallybonded by slimes; but chemically its minute particles, being porouslyheld together, are capable of reacting as separate very fine particles.In this way the reacting system possesses all of the advantages normallyexpected of finely divided solids in their chemical reaction with thefluidizing gases, without the usually attendant disadvantages such as,for example, high rates of dust loss.

The application of the present invention to the selective sulfateroasting of nickeliferous pyrrhotite follows logically in that thefinely divided nickeliferous pyrrhotite concentrate can be made uptogether with the proper proportion of sodium sulfate and sufficientwater to form a slurry of, say, 70% solids, and which can be pumped intothe fluidized bed roasting furnace in accordance with the principles ofthe present invention. In an operation of this type a slurry wasprepared by mixing nickeliferous pyrrhotite concentrate of which about97% could be passed through a D-mesh screen and which contained highproportions of slime material together with an aqueous solution ofsodium sulfate in proportions which resulted in a slurry containingabout 70% pyrrhotite, 27% water and 3% NazSOi, all by weight. As in thecase previously described, the slurry was fed to the fluidized bedroasting furnace through a feed tube constructed from a length ofstandard s" pipe projecting through the centre of the furnace roof. Theslurry feed rate was held at between 4 and 5 lbs. per minute, andatomizing compressed air was introduced with the slurry at a rate of 4standard cubic feet per minute. As before, the sprayed slurry particleswere subjected to a fall of about 111/2 feet, this being the verticaldistance between the tip of the feed tube and the surface of thefluidized bed. Air was introduced at the bottom of the bed at the rateof approximately 24 standard cubic feet per minute per square foot ofhearth area, maintaining the bed in a state of turbulent uidity. Thetemperatures of the freeboard gases and of the iluidized bed were 550 C.and 675 C., respectively. In this operation the proportion of solidmaterial carried over with the furnace gases in the form of `dust waseven smaller than that obtaining in the previously Vdescribed operationin which sodium sulfate was not yused. The recovered dust wascontinuously returned to'the--fluidized bed, and calcine withdrawal wasmaintainedat -a continuous rate compatible with themaintenance"ofasteadybed level. The calcines which resulted from thistreatment yielded the following screen analysis;

16 Table II Mesh: Weight percent A comparison of the random particlesize distribution indicated in Table II with that shown in Table Idemonstrates the extent to which the presence of sodium sulfate enhancesthe agglomerative action of the slime fraction occurring in the feed tothe fluidized bed roasting furnace. As in the previous case, the bedmaterial represented by the screen analysis given in Table II wasadmirably suited to the uidized bed operation, from the standpoint ofboth mechanical and metallurgical requirements. The calcines representedby Table II were leached with water in a countercurrent decantationsystem, and the following metallurgical data resulted:

Comparison of the above nickel extraction ligure, which resulted fromthe roasting of pyrrohotite containing about 4% sodium sulfate, withthose given earlier in this specification indicates that the proportionof sodium sulfate can -be considerably reduced from the previous figureof about 8%, without incurring further loss of nickel in the leachresidue. In other Words, the treatment of the pyrrhotite with an aqueoussolution of sodium sulfate to form a slurry which is fed to the roaster,in accordance with the principles of the present invention, doubles theefficiency of the salt by permitting a high degree of intimacy ofcontact between the salt and the pyrrhotite particles comprising theindividual agglomerates.

The screen analysis of the leached residue was as follows:

The agglomerate size distribution of the leached residue given in TableIV will be recognized by those skilled in the art to be significantlyadvantageous in consideration of the leaching, washing and filteringoperations which are a necessary part of Yall hydrometallurgicalprocesses. Whereas the initial feed to the roaster was in such a linestate of subdivision that 97% could be passed through a 200-mesh screen,less than 25% of the nal product was of this lineness. Thus theadvantage of relatively dustfree operation in the fluidized bed roastingsystem is, by the practice of the present invention, carried through to17 the leaching, washing and filtering steps in roast leach processes,of which the foregoing is merely an example, by providing calcines whichare easy to handle because of their relatively coarse nature.

Further advantages which the new technique of feeding sulde slurries toa uidized bed roasting furnace by spraying them downward through thefurnace freeboard from the top of the furnace displays over conventionalmethods are perhaps better understood by a consideration of the behaviorof a single slurry droplet in its descent through the hot gases in thefurnace chamber. Upon encountering the gases at the top of the chamber,the droplet rapidly reaches a temperature above the boiling point of itscontained water or solution. Since steam is therefore emitted from thedroplet during its fall, the concentration of water vapor or steam inthe furnace gases is greater in the upper regions of the chamber than atany other level in the freeboard. Correspondingly, the concentration offurnace gases other than water vapor, such as oxygen, sulfur dioxide andsulfur trioxide is higher at the level of the bed surface than at thepoint at which the slurry is introduced into the furnace chamber. lt canthus be readily seen that the gases which are chemically effective inthe roasting reactions taking place in the fiuidized bed suffer nodilution by steam when the contained water is eliminated from the slurrybefore, rather than after, it reaches the bed.

The above observations concerning the variable gaseous diluting effectof the water vapor which is a product of the dehydration of a slurryagglomerate during its descent through the furnace freeboard can beextended to the thermal dilution which occurs by virtue of the latentheat of vaporization of the water of the slurry, and the heat capacityof the steam. It may be helpful to consider, for purposes ofillustration, (a) the placing of a fresh slurry agglomerate directly onthe fluidized roasting bed and (b) the falling of a similar agglomeratethrough the freeboard gases before it encounters the bed. In the firstinstance, the contained water is vaporized at bed temperature, the vaporso formed removing a certain quantity of heat from the bed yas it passesupward with the other gaseous roaster products. In the second instance,the heat required for the volatilization of the contained water isabstracted from the gases after they have left the fluidized bed; inother words, the Water in the slurry has lowered the temperature of thegases, while that of the bed remains unaffected.

It is, therefore, evident that the feeding of sulfide slurry to afluidized bed roasting furnace in accordance with the present invention4results in an improvement in heat balance in addition to the advantageswhich have been described earlier in this specification. Such animproved heat balance is a significant factor in certain processes whichhave as their object the selective sulfate roasting of ores orconcentrates in iiuidized bed roasting furnaces in that the minimum feedrate compatible with the required bed temperature corresponds to themaximum average retention time of the solid particles in the fluidizedbed. In other words, since under normal operating conditions, calcinesare removed from the fluidized bed at the same rate as that `at vwhichfeed is introduced, the average retention or treatment time of theroasting solids is an in- Verse function of the feed rate, and thereforeany means by which the feed rate can be reduced increases the extent towhich reactions are completed by increasing the treatment time. "Itfollows, then, that in the autogenous fluidized bed sulfide roastingprocesses with which this invention is concerned, improvements in heatbalance brought about by the practice of the invention result in longersolids retention time, and hence in more completely reacted calcines.

The water vapor which forms when a slurry droplet dries also increasesthe total volume of the furnace gases, and, at any given temperaturebrings about a corresponding increase in the space velocity of theuprising gases.

Since dust carryover is a function of the linear space velocity of thefurnace gases, it is in the interest of good operation to keep the spacevelocity as low as is practicable. The direct addition of slurry to theuidized bed obviously increases the space velocity, and hence the dustVload, of the gases passing upwardly through the bed, whereas when slurrydehydration takes place in the freeboard zone, the space velocity in thebed remains unaffected. Moreover, any increase in the mass of thefreeboard gases due to slurry water vapor is not accompanied by acorresponding increase in volume and space velocity because of thecounteracting shrinkage which is brought about by the cooling effect ofthe slurry on the gases. Thus the previously described advantages of theinvention relating to the effective removal of dust as such by itsadherence to moist slurry particles are augmented by the reduced extentto which dust is allowed to leave the uidized bed by gaseousentrainment.

Still further advantages which the invention has over the conventionalmethods of slurry feeding to fiuidized bed roasting furnaces will beapparent to those skilled in this art in consideration of the widevariety of slimy and adhesive materials which may be included in sulfideslurries in the practice of the present invention. For example, incopper roast-leach processes, in which it is required to selectivelysulfate-roast sulfide-bearing slurries in furnaces of the fluidized bedtype, the presence of oxidized copper minerals in the slurry hasheretofore been disadvantageous because of the tendency of such mineralsto overgrin'ding in the prior milling treatment, with the consequentoccurrence of slimes which would result in the formation ofde-fluidizing lumps in the roasting bed. Such oxidized slime-bearingsulfide slurries are easily and successfully treated when fed tothefluidized bed roaster in accordance with the principle of the presentinvention.

Similarly, it can happen that such a slurry is deficient in the sulfurwhich is required, in practice, to form sulfates of all of the copperpresent, even though thermal requirements are satisfied, in which caseit might be desirable to make up the sulfur deficiency by the additionto the slurry of spent or waste electrolyte which contains sulfuric`acid and iron sulfate. Again, the addition of such solutions would be ahazardous undertaking if the mixture were to be fed to the fluidized bedaccording to conventional methods, but would be eminently practicable inapplication of the present invention.

Another, perhaps more striking, way in which the principles of thisinvention .can be applied is in the liuidized bed roasting 0f ores orconcentrates which do not, at the outset, contain significantproportions of slime material. For example, certain pyritic flotationconcentrates containing lead, zinc and copper were mixed with about 0.75percent sodium sulfate and subjected to a selective sulfating roast in afluidized bed roasting furnace. Since the concentrates containednegligible quantities of slimes and only a minor addition of watersoluble material, little, if any, intergranular agglomeration tookplace, and dust carryover and losses were relatively high. Moreover,fluidization characteristics of the bed thus produced were poor. In thiscase it proved advantageous actually to add as slime material a suitableargillaceous substance, such as bentonite, to the concentrate, in orderto effect the intergranular bonding or agglomerative action with whichthe present invention is concerned.

Not only did the deliberate addition of slimes sharply reduce theproportion of bed material carried over as dust, but it also broughtabout a decided improvement in metallurgical efficiency, as shown incomparison of the following data which resulted from two experiments inwhich a pyritic lead, zinc and copper concentrate was subjected tofluidized bed roasting treatment, the calcines being leached with dilutesulfuric acid. Conditions of the two tests were identical except asnoted below:

The above figures show that the addition of 2% bentonite not onlyimproved the extraction of the desired metals, but also resulted in acleaner separation between the zinc and copper on the one hand, `and theiron of the concentrate on the other hand.

Not only in the field of selective sulfate roasting, but also inprocesses in which simple oxidation is the end in view, can theinvention be profitably applied. For instance, certain types of sulfideand/or sulfarsenide flotation concentrates contain gold, partly in afree-milling form and partly in a refractory, or locked form. In such aninstance, it is desirable to extract the freemilling" gold by extremelyfine grinding of the concentrate, followed by amalgamation or cyanideleaching. The residue resulting from such a treatment is then roasted inorder to free the locked fraction of the gold for its extraction by asecond cyanide leaching treatment, and it is in its application to theliuidized bed roasting of such finely divided slime-bearing materialsthat this process can be used to advantage.

The above two examples, among others described herein, are, it isbelieved, fairly representative of many further useful applications ofthe invention which will doubtless occur to those skilled in this art.In the present specification the terms slirnes and slime particles aremeant to include particles of suldes or oxide minerals, especially thoseof a taley or argillaceous nature, of extremely fine particle size,colloidal or near colloidal dimensions, as Well as the materialsgenerally referred to as gelatinous hydroxide precipitates such as thoseproduced by the addition of alkalis to solutions which contain salts ofmetals such as iron or aluminum. The term water-soluble materials ismeant to include any water soluble inorganic salt, acid or alkali, aswell as such inorganic water soluble material as it may proveadvantageous to add to a sulde slurry in the practice of this invention.

I claim:

1. In the method of roasting nickeliferous sulfide, such asnickeliferous pyrrhotite, concentrates, the improvement which comprisesmaintaining a hot liuidized bed of agglomerates in which roasting takesplace autogenously and from which hot roasting gases rise continuouslyinto the freeboard space above the bed, spraying an aqueous slurrycontaining the nickeliferous sulfide concentrates and a binding agentwith compressed air into the freeboard space to produce a multiplicityof small droplets containing a plurality of the concentrate particleswhich descend downwardly through said freeboard space in countercurrentclon-tact with the rising hot gases from the bed, the hot gases firstevaporating Water from the droplets to convert them into wetagglomerates in which the concentrate particles are bonded by thebinding agent and then evaporating water from the wet agglomerates toform dry agglomerates which on continued descent through the hot gasesenter the liuidized bed, venting the resulting mixture of vapors andgases from the upper portion of the freeboard space, and removing theagglomerates from the liuidized bed after they have been roastedtherein.

2. Method according to claim l, in which ythe aqueous liquid forpreparing the slurry contains an alkali metal salt. f

3. Method according to claim l, in which Ithe aqueous liquid forpreparing the slurry contains sodium sulfate.

4. Method according to claim 1, in which the spraying of the slurry isconductedV wholly in the freeboard space 2? of a roasting chamber havinga roof and at least one side wall to prevent contact of slurry with theroof and side Wall of the roasting chamber and hence to avoid sulfideaccretions thereon.

5. Method according to claim 1, in which the temperature of thefreeboard space is regulated by spraying regulated amounts of water,other than and 'separate from that contained in the slurry, into thefreeboard space; the sprayed water is vaporized completely in thefreeboard space so that it cannot reach and wet the tluidized bed; andthe resulting water vapor is admixed with said vapors and gases ventedfrom ethe freeboard space.

6. Method according to claim 1, in which dust and fines entrained in thehot gases rising from the fiuidized bed are brought in contact with thesprayed slurry and the freshly formed agglomerates; and a substantialamount of the dust and fines adhere to the agglomerates descendingthrough the freeboard space to the bed instead of escaping from thefreeboard space with the vapors and gases.

7. Method according to claim l, in which dust and fines are separatedfrom the mixture of vapors and gases vented from the upper portion ofthe freeboard space; the dust and fines are collected and returned tothe fluidized bed for further treatment; and the vapors and gases freedfrom the dust and fines are vented to the open atmosphere. ,i

8. Method according to claim 1, in which the concentrate particles areextremely small to inhibit kernel roasting.

9*. Method according to claim l, in which the concentrate particles aresufficiently small to pass for the most part through a 20G-mesh screento inhibit kernel roasting.

10. Method according to claim l, in which the agglomerates are of randomsize and sufficiently small to pass for the most part through a 4-meshscreen.

11. Method according t0 claim 1, in which the agglomerates aresuiiiciently small to pass in graded portions through a series ofscreens between about 4 to about mesh to provide random sizes conduciveto goed fiuidity in the bed.

12. Method according to claim 1in which the roasting operation iscontinued in the presence of a sulfating agent until substantially allof the sulfides of nickel, cobalt and copper present in the agglomeratesare converted into water-soluble sulfates of those metals andsubstantially all of the sulfideY of iron present in the agglomerates isconverted into water-insoluble oxide of iron.

13. Method according to claim 1, in which the concentrate particles areextremely small to inhibit kernel roasting; the roasting operation iscontinued in the presence of a sulfating agent until substantially allof the sulfides of nickel, cobalt and copper present in the agglomeratesare converted into water-soluble sulfates of those metals andsubstantially all of the sulfide of iron present in the agglomerates isconverted into water-insoluble oxide of iron.

14. Method according to claim l, in which the concentrateY particles areextremely small to inhibit kernel roasting; the agglomerates are ofrandom size and sufficiently small to pass for the most part through a4-mesh-screen; the roasting operation is continued in the presence of asulfating agent until substantially all of the suliides of nickel,cobalt and copper present in the agglomerates are converted intowater-soluble sulfates of those metals and substantially all of thesulfide of iron present in the agglomerates is converted intoWater-insoluble oxide of iron.

15. Method according to claim 1, in which the concentrate particles aresufiiciently small to pass for the most part through a 20G-mesh screento-inhibit kernel roasting; the roasting operation is continued in thepresence of a sulfating agent until substantially all of the sullides ofnickel, cobalt and copper present inthe agglomerates are con- 21 vertedinto Water-soluble sulfates of those metals and substantially all of thesulfide of iron present in the agglomerates is converted intowater-insoluble oxide of iron.

16. Method according to claim 1, in which the aqueous liquid forpreparing the slurry contains sodium sulfate; the concentrate particlesare extremely small to inhibit kernel roasting; the agglomerates are ofrandom size and sufiiciently small to pass for the most part through a4-mesh screen; the roasting operation is continued until substantiallyall of the sulfides of nickel, cobalt and copper present in theagglomerates are converted into water-soluble sulfates of those metalsand substantially all of the sulfide of iron present in the agglomeratesis converted into waterinsoluble oxide of iron.

17. Method according to claim l, in which the aqueous liquid forpreparing the slurry contains sodium sulfate; the concentrate particlesare suliciently small to pass for the most part through a ZOO-meshscreen to inhibit kernel roasting; the roasting operation is continueduntil substantially all of the sulfdes of nickel, cobalt and copperpresent in the agglomerates are converted into water- 22 solublesulfates of those metals and substantially all of the sulfide of ironpresent in the agglomerates is converted into Water-insoluble oxide ofiron.

18. Method according to claim l, in which the aqueous liquid forpreparing the slurry contains sodium sulfate; the agglomerates aresuicientlysrnall to pass in graded portions through a series of screensbetween about 4 to about 100 mesh to provide random sizes conducive togood fluidity in the bed; and the roasting operation is continued untilsubstantially all of the sulfides of nickel, cobalt and copper presentin the agglomerates are converted into water-soluble sulfates of thosemetals and substantially all of the sulfide of iron present in theagglomerates is converted into water-insoluble oxide of iron.

References Cited in the file of this patent UNITED STATES PATENTS2,090,388 Hardiek Aug. 17, 1937 2,094,275 Mitchell Sept. 28, 19372,475,984 Owen July 12, 1949 2,677,608 McKay et al. May 4, 1954 Nov. l2,1957 F. MATHIEU 2,813,017

THERMAL PROCESS FOR PRODUCING ALKALI METALS AND MAGNESIUM Filed Aug. 26.1955 f INVENTOR Frangos Mafheu.

ATTORNEY

1. IN THE METHOD OF ROASTING NICKELIFEROUS SULFIDE, SUCH ASNICKELIFEROUS PYRRHOTITE CONCENTRATES, THE IMPROVEMENT WHICH COMPRISESMAINTAINING A HOT FLUIDIZED BED OF AGGLOMERATES IN WHICH ROASTING TAKESPLACE AUTOGENOUSLY AND FROM WHICH HOT ROASTING GASES RISE CONTINUOUSLYINTO THE FREEBOARD SPACE ABOVE THE BED, SPRAYING AN AQUEOUS SLURRYCONTAINING THE NICKELIFEROUS SULFIDE CONCENTRATES AND A BINDING AGENTWITH COMPRESSED AIR INTO THE FREEBOARD SPACE TO PRODUCE A MULTIPLICITYOF SMALL DROPLETS CONTAINING A PLURALITY OF THE CONCENTRATE PARTICLESWHICH DECEND DOWNWARDLY THROUGH SAID FREEBOARD SPACE IN COUNTERCURRENTCONTACT WITH THE RISING HOT GASES FROM THE BED, THE HOT GASES FIRSTEVAPORATING WATER FROM THE DROPLETS TO CONVERT THEM INTO WETAGGLOMERATES IN WHICH THE CONCENTRATE PARTICLES ARE BONDED BY THEBINDING AGENT AND THEN EVAPORATING WATER FROM THE WET AGGLOMERATES TOFORM DRY AGGLOMERATES WHICH ON CONTINUED DESCENT THROUGH THE HOT GASESENTER THE FLUIDIZED BED VENTING THE RESULTING MIXTURE OF VAPORS ALNDGASES FROM THE UPPER PORTION OF THE FREEBOARD SPACE, AND REMOVING THEAGGLOMERATES FROM THE FLUIDIZED BED AFTER THEY HAVE BEEN ROASTEDTHEREIN.